Trichomonas is the number one, non-viral sexually transmitted disease worldwide. Infection with Trichomonas vaginal has consequences for women's health, including predisposition to HIV, cervical cancer, and complications of pregnancy. The long-term goal of the research team is to understand the pathogenesis of trichomonosis. The objective of this particular application is to understand the regulation of expression and mechanism of phenotypic variation of the immunogenic protein P270. The rationale for undertaking such studies is that, if P270 can be stably up-regulated on the surface of trichomonads, the parasite will become more susceptible to elimination by antibody. Our central hypothesis to be tested is that a combination of parasitic and host environmental factors affect production and surface expression of the P270 protein. Our current working model is that, by modulating expression and surface placement of P270, the parasite avoids host antibody-mediated destruction. Our studies have shown that high amounts of anti-P270 monoclonal and polyclonal antibody is cytolytic for trichomonads that express surface P270. These findings provide the foundation that will be build upon during the proposed funding period by investigating the following three specific aims. Aim I. To continue characterization of P270 and initiate analysis of novel trichomonad gene(s) with sequence homology to P270 by a) cloning and characterizing the p270 gene with specific focus on the unique, non-repeat sequence among fresh clinical T. vaginal isolates, b) evaluating p270 gene and protein expression, and c) characterizing the newly discovered seq1 and seq2 trichomonad genes that resemble P270. Aim 2. To understand the role of iron deprivation and augmentation and other environmental factors on surface expression of P270 by a) confirming and characterizing iron modulation of surface expression of P270 by a) confirming and characterizing iron modulation of surface expression of P270, b) identifying alternative (non-iron) host factors that regulate surface expression of P270, and c) determining a relationship between phosphorylation and surface expression of P270. Aim 3. TO begin to identify sequences that influence expression of the p270 gene by a) identifying specific p270 gene sequences that contribute to regulation of expression of p270 gene, b) performing comparative analysis of p270 gene regulatory sequences with those of other genes resembling p270, and c) determining whether differential p270 gene expression accounts for varying levels of mRNA among virus-harboring and virus-minus organisms.